SEAL FACE PROPERTIES

FOR A SEAL TO WORK… FACE FLATNESS SEAL FACES ARE TO BE FLAT TO ONE LIGHT BAND OF A HEILIUM ARC LAMP REFLECTED THROUGH A QUARTZ REFERENCE OPTICAL FLAT ONE LIGHT BAND = 0.0000116 INCHES OR 11.6 ONE MILLIONTHS OF AN INCH

Optically Flat Faces 100 psi 0 psi Rotary Face Stationary

FOR A SEAL TO WORK… FACE LUBRICATION BOUNDARY LAYER FILM OF LIQUID FILLS PORES AND IMPERFECTIONS. IT IS PROVIDED BY THE LIQUID IN THE STUFFING BOX. DRY RUNNING OF A PUMP SEAL FOR ONLY A FEW SECONDS MAY DESTROY IT. UNLESS IT IS DESIGNED THAT WAY!

Microscopic Face Lubrication 100 psi Rotary Face Stationary Face 0 psi

Pressure Drop 100 psi 0 psi

Pressure Drop & Vaporization 100 psi 0 psi 25 psi 50 psi Liquid Liquid + Vapor Vapor + Liquid Vapor

Convergent Seal Faces 100 psi 0 psi Rotary Face Stationary

Convergent Seal Faces 100 psi 0 psi Rotary Face Stationary

Convergent Seal Faces 100 psi 0 psi Rotary Face Stationary

Divergent Seal Faces 100 psi 0 psi Rotary Face Stationary

Divergent Seal Faces 100 psi 0 psi Rotary Face Stationary

Divergent Seal Faces 100 psi Rotary Face Stationary Face 0 psi

SEAL BALANCE

Balance Line Unbalanced Seal Face OD Line Face ID Line

BALANCED VS. NON-BALANCED When speaking of “Balance” in reference to mechanical seals, we are not talking about Mechanical or Rotational Balance. Instead, we are referring to Hydraulic Balance. Since mechanical seals are subject to stuffing box pressure, this pressure is utilized to achieve and maintain seal face closure in a non-balanced seal. If stuffing box pressure is very high, typically over 100psi., then the closing force may be too great to allow the “Boundary Layer Liquid” that lubricates the faces to be sufficient and the faces will wear prematurely. A balanced seal compensates for higher pressures by locating the seal faces such that stuffing box pressure has less effect on face closure.

Seal Balance

Face OD Line Face ID Line Balance Line A non-balanced seal has faces located outside the “Balance Diameter” of the seal. Stuffing box pressure is applied to the faces virtually evenly. Face OD Line Face ID Line Balance Line

Unbalanced Seal Face Areas Green+Red=Pressure Area Green+Purple=Face Contact Area Balance Line Face ID Line Face OD Line

Face OD Line Balance Line Face ID Line The faces of a balanced seal are located so that a portion of the face contact occurs inside the balance diameter resulting in reduced closing force due to stuffing box pressure. Face OD Line Balance Line Face ID Line

Balanced Seal Face Areas Green+Red=Pressure Area Red+Purple=Balanced Area Balance Line Face ID Line Face OD Line

Face OD Line Balance Line Face ID Line Most metal bellows seals are balanced. Face OD Line Balance Line Face ID Line

END SEAL FACE PROPERTIES